Selective promotion of different modes of methanol adsorption via the cation substitutional doping of a ZnOimage surface

We used density functional theory to examine how doping the surface of an oxide (i.e., substituting a cation in the surface layer of the metal oxide with a different cation) modifies its chemical properties. As an example, we used the ZnOimage surface doped with Na, K, Au, Ag, Cu, Ti, Al, or Mg and the adsorption of methanol to probe the chemistry of the doped surface. We calculated the binding energies of the possible adsorption products. When we say that methanol preferred to form a certain product, we mean that the product had the lowest energy of formation from gas-phase methanol and the surface. We found that on a surface doped with Na or K, CH3OH preferred to dissociate into adsorbed formaldehyde and two hydroxyls on the surface. On the Ti- or Al-doped surfaces, methanol dissociated by forming a methoxy radical bound to the dopant and a hydroxyl on an oxygen atom near the dopant. On the undoped oxide or on ZnO doped with Au, Cu, Ag, or Mg, methanol preferred to adsorb molecularly. The Au, Cu, Ag, or Mg dopants exhibited no significant preference for one adsorption mode over the others. Our most important qualitative conclusion is that doping can significantly alter the chemistry of an oxide surface, offering an avenue for designing catalysts that have better performance than undoped oxides.